Well after 4 days and no returned calls, I finally got a rep today. "Joe" said the reason the Mobil 1 was turning black was because Mobil changed the formula. I was advised to switch to the Exmark hydraulic fluid, which I was previously advised not to use in my 2008 pumps, and I could double the service interval to 400 hours. I was advised that it is okay to mix the fluids. Does anyone else have experience mixing these fluids? I am in the market for a new mower but have my doubts about another Exmark after this experience. Does anyone have a positive experience with another manufactures tech support services? I am currently looking at Gravely, Bobcat and Scag eqipment.